Is the course of the cervicofacial division of the facial nerve consistent with the adjacent vessels?

Abstract Individual facial nerve branching patterns can be difficult to predict. The superficial course of its terminal branches poses them at risk of injury during head and neck surgeries. We report the rare course of a branch of the facial nerve deep into the posterior facial vein.


| CASE PRESENTATION
A rare course of the inferior division of the extratemporal facial nerve was observed during the dissection of a 75-year-old Caucasian female formalin embalmed Greek cadaver, donated to the Department of Anatomy, Aristotle University of Thessaloniki for teaching and research purposes. Heart attack was reported as the cause of death. No gross pathology or tumor formation was observed during the routine dissection of the head and neck region. The full dissection of the extratemporal portion of the facial nerve-after removal of the superficial lobe of the parotid gland-was the objective of the dissection, in an effort to map facial nerve branching patterns in the Greek population. The branching pattern of the facial nerve was type VI bilaterally according to Davis classification. On the left side, the inferior division of the main trunk (cervicofacial segment) was superficial to the retromandibular vein as usual. After giving an anastomotic branch to the buccal branch of the facial nerve a bifurcation was noted. The upper branch ran superficial to the posterior facial vein providing nerve supply to the corresponding angular oris muscle. The lower branch ran deep to the posterior facial vein and in the further 0.2 cm, it was divided into an upper marginal and a lower cervical branch ( Figure 1). External jugular vein was coursed underneath the above bifurcation of the lower branch of facial nerve. Every branch of the facial nerve crossed horizontally beneath the investing layer of the deep cervical fascia and above the masseter muscle. No other anatomic variations were recorded. To the best of our knowledge, this is a very rare course of the inferior division of the facial nerve. All physicians and especially surgeons involved in the treatment of this area should be aware of all possible variations in order to ensure a safe diagnosis and an uneventful procedure in parotid or facial plastic surgery cases.
The extratemporal portion of the facial nerve presents a wide anatomic variability with anastomotic branches and various branching patterns. Davis classification still remains the most popular one, although many researchers did suggest other classifications. 1 The analysis of anatomical variations contributes to obtaining an actual image of the human body inside, which is crucial in everyday clinical practice. 2 Deep knowledge of the head and neck anatomy is a prerequisite in order to proceed to an uneventful and safe parotid surgery. Injury to the facial nerve leads to temporary or permanent palsy, with both functional and cosmetic sequelae. A safe superficial parotidectomy is performed after full facial neck dissection and excision of the tissue overlying the nerve. 3 The retromandibular vein is the most consistent radiological landmark between the superficial and deep lobe of the parotid gland. Facial nerve superficial to the retromandibular vein and to the posterior facial vein. Thus, an anatomical variation with the nerve running beneath the posterior facial vein may lead to a risky dissection during parotid surgery and to an inadvertent injury after ligation of the external jugular vein. The presented variation highlights and augments the necessity of a meticulous dissection taking into account the highly possible presence of an underlying aberrancy.

FUNDING INFORMATION
None.

CONFLICT OF INTEREST STATEMENT
No potential conflict of interest was reported by the authors.

DATA AVAILABILITY STATEMENT
Data are available from the corresponding author with the permission of Aristotle University of Thessaloniki. The data that support the findings of this study are available from the corresponding author upon reasonable request.

ETHICS STATEMENT
This is a cadaveric study. The cadaver was donated to our department for scientific and research purposes in a cadaver donation program, after the written consent of the relatives of the cadaver.

CONSENT
Written informed consent was obtained from the patient to publish this report in accordance with the journal's patient consent policy.